Medieval times: A perfect storm of hurricane activity

We know there was an unusual burst of tropical storm activity in the Atlantic over the past decade. But the historical record only goes back 150 years or so. How would we be able to get a broader perspective?

A weather researcher claims to have figured out a way to look back 1,500 years by analyzing sediment samples and other climate data. His results were published in the August 13 issue of the journalNature.

Michael Mann, a professor of meteorology at Penn State, concludes that a medieval climate anomaly occurred a thousand years ago, ratcheting up hurricane activity in the Atlantic between 900 A.D. and 1100 A.D. He says the recent higher level of hurricane activity is similar.

“We are at levels now that are about as high as anything we have seen in the past 1,000 years,” Mann says in a Penn State press release.

Mann and colleagues used two different approaches to gauge tropical storm activity – one sifting through sediment left by land falling hurricanes that caused a storm surge, breached a beach area and left a deposit.

The second method was based on a common statistical model that predicts hurricane activity based on climate variables, such as reconstructed sea surface temperatures. The climate cocktail to create the perfect storm period includes warm sea temperatures combined with La Nina conditions – the opposite of the El Nino conditions that are influencing this hurricane season.

The meteorologists reported that results using both approaches were similar, with one corroborating the other.

Naturally, this is fueling another round of debate on global warming.

“It seems that the paleodata support the contention that greenhouse warming may increase the frequency of Atlantic tropical storms,” Mann says. “It may not be just that the storms are stronger, but that there are there may be more of them as well.”

But what caused the ocean temperature rise a thousand years ago? This would have been a naturally occurring phenomenon.

If you’d like look into the issue further, check out this interesting 25-minute Web interview with Mann, posted by the National Science Foundation (NSF).

TROPICAL UPDATE: Hurricane Bill slammed Nova Scotia and Newfoundland in Canada yesterday, knocking out power to about 40,000 in Nova Scotia and washing out some roads, according to The Telegram in St. John’s. One low-lying coastal community in Newfoundland was evacuated, but officials said the storm, which had been downgraded to a tropical storm, was weaker than expected. It raced through at 30 mph and is no longer a tropical system.

Closer to South Florida, a cluster of storms nearing the northern Antilles could develop into the season’s fourth tropical storm – Danny, if it makes it – near the Bahamas on Wednesday. Forecasters think it will track north from there and possibly threaten North Carolina.

About the Author

John Nelander is a freelance writer, book editor and publisher in West Palm Beach. Weather Matters features news and observations about the weather with a focus on what's happening in South Florida. The blog also looks at the latest studies on climate change as well as what's happening in the weather forecasting biz. His website is www.pbeditorialservices.com.